In chainstitch sewing machines, and more particularly those which form chainstitches from three threads, there is frequently a tendency to skip stitches. This is primarily due to the fact that the looper thread loop fails to open sufficiently to permit it to be penetrated by the needle at the appropriate point in the sewing cycle. An attempted solution is to arrange the vertical path of the needle such that the needle shank brushes against the looper blade to assure penetration of the thread triangle. Understandably, however, such a solution has its drawbacks. Fast wearing of the needles, damaging of the needle point and undesirable heat build up are but a few of such drawbacks.
U.S. Pat. Nos. 1,702,792 and 1,825,513 along with German Pat. No. 483,989 are all attempts at a solution of this problem. Such devices, however, involve complex mechanisms which do little to increase the size of the thread triangle at the point and time of needle penetration.